1 //===- llvm/Analysis/TargetTransformInfo.h ----------------------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass exposes codegen information to IR-level passes. Every
11 // transformation that uses codegen information is broken into three parts:
12 // 1. The IR-level analysis pass.
13 // 2. The IR-level transformation interface which provides the needed
15 // 3. Codegen-level implementation which uses target-specific hooks.
17 // This file defines #2, which is the interface that IR-level transformations
18 // use for querying the codegen.
20 //===----------------------------------------------------------------------===//
22 #ifndef LLVM_ANALYSIS_TARGETTRANSFORMINFO_H
23 #define LLVM_ANALYSIS_TARGETTRANSFORMINFO_H
25 #include "llvm/IR/Intrinsics.h"
26 #include "llvm/Pass.h"
27 #include "llvm/Support/DataTypes.h"
38 /// TargetTransformInfo - This pass provides access to the codegen
39 /// interfaces that are needed for IR-level transformations.
40 class TargetTransformInfo {
42 /// \brief The TTI instance one level down the stack.
44 /// This is used to implement the default behavior all of the methods which
45 /// is to delegate up through the stack of TTIs until one can answer the
47 TargetTransformInfo *PrevTTI;
49 /// \brief The top of the stack of TTI analyses available.
51 /// This is a convenience routine maintained as TTI analyses become available
52 /// that complements the PrevTTI delegation chain. When one part of an
53 /// analysis pass wants to query another part of the analysis pass it can use
54 /// this to start back at the top of the stack.
55 TargetTransformInfo *TopTTI;
57 /// All pass subclasses must in their initializePass routine call
58 /// pushTTIStack with themselves to update the pointers tracking the previous
59 /// TTI instance in the analysis group's stack, and the top of the analysis
61 void pushTTIStack(Pass *P);
63 /// All pass subclasses must call TargetTransformInfo::getAnalysisUsage.
64 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
67 /// This class is intended to be subclassed by real implementations.
68 virtual ~TargetTransformInfo() = 0;
70 /// \name Generic Target Information
73 /// \brief Underlying constants for 'cost' values in this interface.
75 /// Many APIs in this interface return a cost. This enum defines the
76 /// fundamental values that should be used to interpret (and produce) those
77 /// costs. The costs are returned as an unsigned rather than a member of this
78 /// enumeration because it is expected that the cost of one IR instruction
79 /// may have a multiplicative factor to it or otherwise won't fit directly
80 /// into the enum. Moreover, it is common to sum or average costs which works
81 /// better as simple integral values. Thus this enum only provides constants.
83 /// Note that these costs should usually reflect the intersection of code-size
84 /// cost and execution cost. A free instruction is typically one that folds
85 /// into another instruction. For example, reg-to-reg moves can often be
86 /// skipped by renaming the registers in the CPU, but they still are encoded
87 /// and thus wouldn't be considered 'free' here.
88 enum TargetCostConstants {
89 TCC_Free = 0, ///< Expected to fold away in lowering.
90 TCC_Basic = 1, ///< The cost of a typical 'add' instruction.
91 TCC_Expensive = 4 ///< The cost of a 'div' instruction on x86.
94 /// \brief Estimate the cost of a specific operation when lowered.
96 /// Note that this is designed to work on an arbitrary synthetic opcode, and
97 /// thus work for hypothetical queries before an instruction has even been
98 /// formed. However, this does *not* work for GEPs, and must not be called
99 /// for a GEP instruction. Instead, use the dedicated getGEPCost interface as
100 /// analyzing a GEP's cost required more information.
102 /// Typically only the result type is required, and the operand type can be
103 /// omitted. However, if the opcode is one of the cast instructions, the
104 /// operand type is required.
106 /// The returned cost is defined in terms of \c TargetCostConstants, see its
107 /// comments for a detailed explanation of the cost values.
108 virtual unsigned getOperationCost(unsigned Opcode, Type *Ty,
109 Type *OpTy = nullptr) const;
111 /// \brief Estimate the cost of a GEP operation when lowered.
113 /// The contract for this function is the same as \c getOperationCost except
114 /// that it supports an interface that provides extra information specific to
115 /// the GEP operation.
116 virtual unsigned getGEPCost(const Value *Ptr,
117 ArrayRef<const Value *> Operands) const;
119 /// \brief Estimate the cost of a function call when lowered.
121 /// The contract for this is the same as \c getOperationCost except that it
122 /// supports an interface that provides extra information specific to call
125 /// This is the most basic query for estimating call cost: it only knows the
126 /// function type and (potentially) the number of arguments at the call site.
127 /// The latter is only interesting for varargs function types.
128 virtual unsigned getCallCost(FunctionType *FTy, int NumArgs = -1) const;
130 /// \brief Estimate the cost of calling a specific function when lowered.
132 /// This overload adds the ability to reason about the particular function
133 /// being called in the event it is a library call with special lowering.
134 virtual unsigned getCallCost(const Function *F, int NumArgs = -1) const;
136 /// \brief Estimate the cost of calling a specific function when lowered.
138 /// This overload allows specifying a set of candidate argument values.
139 virtual unsigned getCallCost(const Function *F,
140 ArrayRef<const Value *> Arguments) const;
142 /// \brief Estimate the cost of an intrinsic when lowered.
144 /// Mirrors the \c getCallCost method but uses an intrinsic identifier.
145 virtual unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
146 ArrayRef<Type *> ParamTys) const;
148 /// \brief Estimate the cost of an intrinsic when lowered.
150 /// Mirrors the \c getCallCost method but uses an intrinsic identifier.
151 virtual unsigned getIntrinsicCost(Intrinsic::ID IID, Type *RetTy,
152 ArrayRef<const Value *> Arguments) const;
154 /// \brief Estimate the cost of a given IR user when lowered.
156 /// This can estimate the cost of either a ConstantExpr or Instruction when
157 /// lowered. It has two primary advantages over the \c getOperationCost and
158 /// \c getGEPCost above, and one significant disadvantage: it can only be
159 /// used when the IR construct has already been formed.
161 /// The advantages are that it can inspect the SSA use graph to reason more
162 /// accurately about the cost. For example, all-constant-GEPs can often be
163 /// folded into a load or other instruction, but if they are used in some
164 /// other context they may not be folded. This routine can distinguish such
167 /// The returned cost is defined in terms of \c TargetCostConstants, see its
168 /// comments for a detailed explanation of the cost values.
169 virtual unsigned getUserCost(const User *U) const;
171 /// \brief hasBranchDivergence - Return true if branch divergence exists.
172 /// Branch divergence has a significantly negative impact on GPU performance
173 /// when threads in the same wavefront take different paths due to conditional
175 virtual bool hasBranchDivergence() const;
177 /// \brief Test whether calls to a function lower to actual program function
180 /// The idea is to test whether the program is likely to require a 'call'
181 /// instruction or equivalent in order to call the given function.
183 /// FIXME: It's not clear that this is a good or useful query API. Client's
184 /// should probably move to simpler cost metrics using the above.
185 /// Alternatively, we could split the cost interface into distinct code-size
186 /// and execution-speed costs. This would allow modelling the core of this
187 /// query more accurately as a call is a single small instruction, but
188 /// incurs significant execution cost.
189 virtual bool isLoweredToCall(const Function *F) const;
191 /// Parameters that control the generic loop unrolling transformation.
192 struct UnrollingPreferences {
193 /// The cost threshold for the unrolled loop, compared to
194 /// CodeMetrics.NumInsts aggregated over all basic blocks in the loop body.
195 /// The unrolling factor is set such that the unrolled loop body does not
196 /// exceed this cost. Set this to UINT_MAX to disable the loop body cost
199 /// The cost threshold for the unrolled loop when optimizing for size (set
200 /// to UINT_MAX to disable).
201 unsigned OptSizeThreshold;
202 /// The cost threshold for the unrolled loop, like Threshold, but used
203 /// for partial/runtime unrolling (set to UINT_MAX to disable).
204 unsigned PartialThreshold;
205 /// The cost threshold for the unrolled loop when optimizing for size, like
206 /// OptSizeThreshold, but used for partial/runtime unrolling (set to UINT_MAX
208 unsigned PartialOptSizeThreshold;
209 /// A forced unrolling factor (the number of concatenated bodies of the
210 /// original loop in the unrolled loop body). When set to 0, the unrolling
211 /// transformation will select an unrolling factor based on the current cost
212 /// threshold and other factors.
214 // Set the maximum unrolling factor. The unrolling factor may be selected
215 // using the appropriate cost threshold, but may not exceed this number
216 // (set to UINT_MAX to disable). This does not apply in cases where the
217 // loop is being fully unrolled.
219 /// Allow partial unrolling (unrolling of loops to expand the size of the
220 /// loop body, not only to eliminate small constant-trip-count loops).
222 /// Allow runtime unrolling (unrolling of loops to expand the size of the
223 /// loop body even when the number of loop iterations is not known at compile
228 /// \brief Get target-customized preferences for the generic loop unrolling
229 /// transformation. The caller will initialize UP with the current
230 /// target-independent defaults.
231 virtual void getUnrollingPreferences(const Function *F, Loop *L,
232 UnrollingPreferences &UP) const;
236 /// \name Scalar Target Information
239 /// \brief Flags indicating the kind of support for population count.
241 /// Compared to the SW implementation, HW support is supposed to
242 /// significantly boost the performance when the population is dense, and it
243 /// may or may not degrade performance if the population is sparse. A HW
244 /// support is considered as "Fast" if it can outperform, or is on a par
245 /// with, SW implementation when the population is sparse; otherwise, it is
246 /// considered as "Slow".
247 enum PopcntSupportKind {
253 /// \brief Return true if the specified immediate is legal add immediate, that
254 /// is the target has add instructions which can add a register with the
255 /// immediate without having to materialize the immediate into a register.
256 virtual bool isLegalAddImmediate(int64_t Imm) const;
258 /// \brief Return true if the specified immediate is legal icmp immediate,
259 /// that is the target has icmp instructions which can compare a register
260 /// against the immediate without having to materialize the immediate into a
262 virtual bool isLegalICmpImmediate(int64_t Imm) const;
264 /// \brief Return true if the addressing mode represented by AM is legal for
265 /// this target, for a load/store of the specified type.
266 /// The type may be VoidTy, in which case only return true if the addressing
267 /// mode is legal for a load/store of any legal type.
268 /// TODO: Handle pre/postinc as well.
269 virtual bool isLegalAddressingMode(Type *Ty, GlobalValue *BaseGV,
270 int64_t BaseOffset, bool HasBaseReg,
271 int64_t Scale) const;
273 /// \brief Return true if the target works with masked instruction
274 /// AVX2 allows masks for consecutive load and store for i32 and i64 elements.
275 /// AVX-512 architecture will also allow masks for non-consecutive memory
277 virtual bool isLegalPredicatedStore(Type *DataType, int Consecutive) const;
278 virtual bool isLegalPredicatedLoad (Type *DataType, int Consecutive) const;
280 /// \brief Return the cost of the scaling factor used in the addressing
281 /// mode represented by AM for this target, for a load/store
282 /// of the specified type.
283 /// If the AM is supported, the return value must be >= 0.
284 /// If the AM is not supported, it returns a negative value.
285 /// TODO: Handle pre/postinc as well.
286 virtual int getScalingFactorCost(Type *Ty, GlobalValue *BaseGV,
287 int64_t BaseOffset, bool HasBaseReg,
288 int64_t Scale) const;
290 /// \brief Return true if it's free to truncate a value of type Ty1 to type
291 /// Ty2. e.g. On x86 it's free to truncate a i32 value in register EAX to i16
292 /// by referencing its sub-register AX.
293 virtual bool isTruncateFree(Type *Ty1, Type *Ty2) const;
295 /// \brief Return true if this type is legal.
296 virtual bool isTypeLegal(Type *Ty) const;
298 /// \brief Returns the target's jmp_buf alignment in bytes.
299 virtual unsigned getJumpBufAlignment() const;
301 /// \brief Returns the target's jmp_buf size in bytes.
302 virtual unsigned getJumpBufSize() const;
304 /// \brief Return true if switches should be turned into lookup tables for the
306 virtual bool shouldBuildLookupTables() const;
308 /// \brief Return hardware support for population count.
309 virtual PopcntSupportKind getPopcntSupport(unsigned IntTyWidthInBit) const;
311 /// \brief Return true if the hardware has a fast square-root instruction.
312 virtual bool haveFastSqrt(Type *Ty) const;
314 /// \brief Return the expected cost of materializing for the given integer
315 /// immediate of the specified type.
316 virtual unsigned getIntImmCost(const APInt &Imm, Type *Ty) const;
318 /// \brief Return the expected cost of materialization for the given integer
319 /// immediate of the specified type for a given instruction. The cost can be
320 /// zero if the immediate can be folded into the specified instruction.
321 virtual unsigned getIntImmCost(unsigned Opc, unsigned Idx, const APInt &Imm,
323 virtual unsigned getIntImmCost(Intrinsic::ID IID, unsigned Idx,
324 const APInt &Imm, Type *Ty) const;
327 /// \name Vector Target Information
330 /// \brief The various kinds of shuffle patterns for vector queries.
332 SK_Broadcast, ///< Broadcast element 0 to all other elements.
333 SK_Reverse, ///< Reverse the order of the vector.
334 SK_Alternate, ///< Choose alternate elements from vector.
335 SK_InsertSubvector, ///< InsertSubvector. Index indicates start offset.
336 SK_ExtractSubvector ///< ExtractSubvector Index indicates start offset.
339 /// \brief Additional information about an operand's possible values.
340 enum OperandValueKind {
341 OK_AnyValue, // Operand can have any value.
342 OK_UniformValue, // Operand is uniform (splat of a value).
343 OK_UniformConstantValue, // Operand is uniform constant.
344 OK_NonUniformConstantValue // Operand is a non uniform constant value.
347 /// \brief Additional properties of an operand's values.
348 enum OperandValueProperties { OP_None = 0, OP_PowerOf2 = 1 };
350 /// \return The number of scalar or vector registers that the target has.
351 /// If 'Vectors' is true, it returns the number of vector registers. If it is
352 /// set to false, it returns the number of scalar registers.
353 virtual unsigned getNumberOfRegisters(bool Vector) const;
355 /// \return The width of the largest scalar or vector register type.
356 virtual unsigned getRegisterBitWidth(bool Vector) const;
358 /// \return The maximum interleave factor that any transform should try to
359 /// perform for this target. This number depends on the level of parallelism
360 /// and the number of execution units in the CPU.
361 virtual unsigned getMaxInterleaveFactor() const;
363 /// \return The expected cost of arithmetic ops, such as mul, xor, fsub, etc.
365 getArithmeticInstrCost(unsigned Opcode, Type *Ty,
366 OperandValueKind Opd1Info = OK_AnyValue,
367 OperandValueKind Opd2Info = OK_AnyValue,
368 OperandValueProperties Opd1PropInfo = OP_None,
369 OperandValueProperties Opd2PropInfo = OP_None) const;
371 /// \return The cost of a shuffle instruction of kind Kind and of type Tp.
372 /// The index and subtype parameters are used by the subvector insertion and
373 /// extraction shuffle kinds.
374 virtual unsigned getShuffleCost(ShuffleKind Kind, Type *Tp, int Index = 0,
375 Type *SubTp = nullptr) const;
377 /// \return The expected cost of cast instructions, such as bitcast, trunc,
379 virtual unsigned getCastInstrCost(unsigned Opcode, Type *Dst,
382 /// \return The expected cost of control-flow related instructions such as
384 virtual unsigned getCFInstrCost(unsigned Opcode) const;
386 /// \returns The expected cost of compare and select instructions.
387 virtual unsigned getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
388 Type *CondTy = nullptr) const;
390 /// \return The expected cost of vector Insert and Extract.
391 /// Use -1 to indicate that there is no information on the index value.
392 virtual unsigned getVectorInstrCost(unsigned Opcode, Type *Val,
393 unsigned Index = -1) const;
395 /// \return The cost of Load and Store instructions.
396 virtual unsigned getMemoryOpCost(unsigned Opcode, Type *Src,
398 unsigned AddressSpace) const;
400 /// \brief Calculate the cost of performing a vector reduction.
402 /// This is the cost of reducing the vector value of type \p Ty to a scalar
403 /// value using the operation denoted by \p Opcode. The form of the reduction
404 /// can either be a pairwise reduction or a reduction that splits the vector
405 /// at every reduction level.
409 /// ((v0+v1), (v2, v3), undef, undef)
412 /// ((v0+v2), (v1+v3), undef, undef)
413 virtual unsigned getReductionCost(unsigned Opcode, Type *Ty,
414 bool IsPairwiseForm) const;
416 /// \returns The cost of Intrinsic instructions.
417 virtual unsigned getIntrinsicInstrCost(Intrinsic::ID ID, Type *RetTy,
418 ArrayRef<Type *> Tys) const;
420 /// \returns The number of pieces into which the provided type must be
421 /// split during legalization. Zero is returned when the answer is unknown.
422 virtual unsigned getNumberOfParts(Type *Tp) const;
424 /// \returns The cost of the address computation. For most targets this can be
425 /// merged into the instruction indexing mode. Some targets might want to
426 /// distinguish between address computation for memory operations on vector
427 /// types and scalar types. Such targets should override this function.
428 /// The 'IsComplex' parameter is a hint that the address computation is likely
429 /// to involve multiple instructions and as such unlikely to be merged into
430 /// the address indexing mode.
431 virtual unsigned getAddressComputationCost(Type *Ty,
432 bool IsComplex = false) const;
434 /// \returns The cost, if any, of keeping values of the given types alive
437 /// Some types may require the use of register classes that do not have
438 /// any callee-saved registers, so would require a spill and fill.
439 virtual unsigned getCostOfKeepingLiveOverCall(ArrayRef<Type*> Tys) const;
443 /// Analysis group identification.
447 /// \brief Create the base case instance of a pass in the TTI analysis group.
449 /// This class provides the base case for the stack of TTI analyzes. It doesn't
450 /// delegate to anything and uses the STTI and VTTI objects passed in to
451 /// satisfy the queries.
452 ImmutablePass *createNoTargetTransformInfoPass();
454 } // End llvm namespace